Solid state lighting arrays are used for many of lighting applications. For example, solid state lighting panels including arrays of solid state lighting devices have been used as direct illumination sources, for example, in architectural and/or accent lighting. A lighting panel may be used, for example, as a backlight unit (BLU) for an LCD display. A solid state BLU may include, for example, a packaged light emitting device including one or more light emitting diodes (LEDs).
LEDs are current-controlled devices in the sense that the intensity of the light emitted from an LED is related to the amount of current driven through the LED. A solid state lighting panel can be configured that can produce, through the use of multiple colors of LEDs and individual intensity control of each color, a variety of color hues. Precise control of color and intensity can involve data intensive and/or iterative processor operations that can require significant processing resources.
One common method for controlling the current driven through the LEDs to achieve desired intensity and color mixing is a Pulse Width Modulation (PWM) scheme. PWM schemes pulse the LEDs alternately to a full current “ON” state followed by a zero current “OFF” state. The ratio of the ON time to the total cycle time is defined as the duty cycle, and, in a fixed cycle frequency, determines the time-average luminous intensity. Varying the duty cycle from 0% to 100% correspondingly varies the intensity of the LED as perceived by the human eye from 0% to 100% because the human eye integrates the ON/OFF pulses into time-average luminous intensity. A processor may be used to generate PWM signals to current drivers.